flang-21: `flang-new` command should be `flang`

[Vinfall]

Quoted from LLVM Fortran Levels Up: Goodbye flang-new, Hello flang! on The LLVM Project Blog:

LLVM has included a Fortran compiler “Flang” since LLVM 11 in late 2020. However, until recently the Flang binary was not flang (like clang) but instead flang-new.

LLVM 20 ends the era of flang-new. The community has decided that Flang is worthy of a new name.

The “new” name? You guessed it, flang.

A simple change that represents a major milestone for Flang.

Just one line of change I guess, not sure if build_option_flang should be changed.

void-packages/srcpkgs/llvm21/template

Lines 922 to 928 in dc1738e

	_flang_files=(
	bin/flang-new
	bin/bbc
	bin/f18-parse-demo
	bin/fir-opt
	bin/tco
	)

void-packages/srcpkgs/llvm21/template

Lines 195 to 198 in dc1738e

	if [ "$build_option_flang" ]; then
	configure_args+=" -DLIBOMP_FORTRAN_MODULES_COMPILER=/${_llvm_bindir}/flang-new"
	configure_args+=" -DCMAKE_Fortran_COMPILER=/${_llvm_bindir}/flang-new"
	fi